1. Field of the Invention
The present invention relates to a control device for a hybrid vehicle that includes an engine and a motor or a motor generator as a driving power source, in particular, a control system for a hybrid vehicle that is configured such that the engine can be disconnected from a transmission system of a driving force.
2. Description of Related Art
A hybrid vehicle that includes both a motor or a motor generator (hereinafter, these are described in block as a motor in some cases) and an engine as a power source has various advantages such that the engine can be stopped (idle stopped) during stoppage, energy can be regenerated by the motor during deceleration, further the engine can be operated at an operation point excellent in the energy efficiency. In particular, when a motor travel time is lengthened, an improvement effect in fuel consumption as a whole vehicle can be increased. This is because, in the case of motor travel, the engine is stopped and a fuel in not consumed. In this case, in order to reduce power loss due to co-rotation of the engine, it is preferable to disconnect the engine from a motor that outputs a driving force for travelling or a power transmission system that transmits the driving force to a wheel. When such a clutch for separating the engine is provided, in the case of motor travel, operation modes such that the engine is stopped or left to travel can be selected. Such a hybrid vehicle provided with a clutch for separating the engine is disclosed in Japanese Patent Application Publication No. 08-295140 (JP 08-295140 A).
According to a simple description of a configuration thereof, in a differential mechanism provided with three rotating elements like a planetary gear system, an electric machine is coupled with a first rotating element, a second rotating element is set as an output element, further a third rotating element is coupled with a braking means. The engine is coupled with the third rotating element via the clutch. Further, the motor is coupled with the second rotating element. Therefore, according to a configuration described in JP 08-295140 A, by fixing the third rotating element by the engine or the braking means, the differential mechanism functions as decelerator or an accelerator. Therefore, by operating the electric machine coupled with the first rotating element as a motor, a torque thereof can be transmitted to an output element. That is, travel by power output from the electric machine and the motor becomes possible. Further, when one-way clutch that engages with the third rotating element when the torque works in a direction that reverses the rotation of the third rotating element and fixes the third rotating element is adopted as the braking means, without relying on the engine during motor travel, the third rotating element can be fixed by the one-way clutch, and further the clutch can be disconnected from the third rotating element, therefore, the engine can be kept driving or be stopped.
Further, Japanese Patent Application Publication No. 2010-215097 (JP 2010-215097 A) discloses a hybrid vehicle that includes a motor that generates a driving force and an engine that is coupled with the motor via a clutch. According to the vehicle described in JP 2010-215097 A, a motor rotational speed and a target clutch torque are set such that a clutch becomes a predetermined slip state, after the target slip state is reached, the target clutch torque is corrected based on a difference between the target clutch torque and a motor torque. More specifically, a rotational speed of the motor is set to the rotational speed for starting the engine, and a target torque of the clutch is set to a torque to be a predetermined slip state. In this state, the target clutch torque is corrected such that a deviation between the motor rotational speed and the engine speed becomes a predetermined value or less. Then, a difference between a motor torque memorized in the course of such control and a torque that is set before start of the control is memorized and, in the control of next time and thereafter, the difference is added to the setting value and the setting value is corrected.
Further, Japanese Patent Application Publication No. 2005-273761 (JP 2005-273761 A) discloses a control device of a hybrid drive device configured such that an engine speed and a first motor generator are coupled via a differential mechanism, an output shaft coupled with an output element of the differential mechanism and a second motor generator are coupled via a transmission mechanism that can perform two-stage speed change, the first motor generator is functioned as an electric machine and the engine speed is controlled to the speed excellent in the fuel consumption, and an electric power generated accompanying this is supplied to the second motor generator, and this is functioned as a motor. Then, the control device described in JP 2005-273761 A is configured to learn a relationship between a torque capacity and an engagement control amount of a frictional engagement device that is provided to the transmission mechanism based on the torque and oil pressure of the clutch for maintaining the rotational speed of the second motor generator at a predetermined value.
Next, Japanese Patent Application Publication No. 2001-112118 (JP 2001-112118 A) discloses a hybrid drive device that includes a brake that couples an engine and a motor via a power dividing mechanism made of a differential mechanism and fixes an output element of the power dividing mechanism, a first clutch that couples the motor with an input shaft of a transmission, and a second clutch that couples the output element with the input shaft of the transmission. According to the device described in this JP 2001-112118 A, an input torque of the transmission in the process of gradually increasing oil pressure of the second clutch is estimated based on the motor torque and a transmission torque capacity of the second clutch.